Voltage transformers have become indispensable to modern life, especially we live in this electric appliance-ridden age, for example, electric appliances, such as walkmans, mobile phones, MP3, notebook computers and so forth are almost in use of voltage transformers. The specifications of voltage transformers are numerous. Some input voltages are 110 volt AC, others are 220 volt AC; the output specifications may further vary from electric appliance to electric appliance and that would generate more different requirements for the output voltages, such as the output voltage required by the voltage transformer of mobile phone chargers may be only 5 volt DC; portable computers may need 19 volt DC; and such as the output voltage required by the voltage transformer of the external computer modem is 12 volt AC.
Nowadays more novel voltage transformers can encompass the full range of input voltages, that is, input voltages from 100 volt AC to 240 volt AC, all the input voltages within this range can be transformed into a fixed output voltage; nevertheless, the output voltage is a fixed voltage, as well as every electric appliance product requires different input voltages, so the voltage transformers corresponding to the output voltages respectively are necessary for meeting the requirement of every electric appliance product.
Today, every ordinary family has at least several even tens of voltage transformers with different sizes and specifications. If there is a function of which various output voltages can be selected in one voltage transformer, thus one voltage transformer can correspond to the voltages required by several different electric appliance products, then, that can significantly decrease the quantity of use of a variety of voltage transformers required, and eliminate unnecessary expenses. In particular, when people go outside carrying many kinds of different electric appliance products, such as traveling abroad or traveling on official business, it is quite cumbersome that every electric appliance product in the baggage is accompanied with a dedicated voltage transformer; if we use this kind of voltage transformer capable of corresponding to various voltage requirements simultaneously at this time, that will lighten the baggage loading effectively and considerably enhance the convenience.
As shown in FIG. 1, it is a common voltage transformer with adjustable multiple voltage outputs in market condition. After a fixed voltage is inputted into the power supply input terminal 11, the power supply output terminal 13 would generate a fixed output voltage via the voltage transformation circuit in the voltage transformer body 12. If it is necessary to change the output voltage, as long as it needs to adjust the output voltage selector 15 on the output voltage selective switch 14 to a corresponding position, then a corresponding output voltage will be generated.
However, such selective switches are easily led to abrasion owing to frequent switching, it makes the positioning effect of switching the voltage selector 15 gradually deviated or imperfectly contacted and causes unstable voltage outputs or even error voltage outputs, when serious circumstances occur, it will result in damage of electric appliances. In particular, since most output voltage values are simply labeled by stickers, they might displace or fall off due to long-term use as well, that further misleads consumers and then generates error outputs.
Besides, some dealers have incorporated guide tabs, which contained different circuit elements into the same voltage transformation circuits and thereby created prospective voltage transformation effect. However, the jacks and terminals exposed to the air are accessible to be affected by moisture due to weather and gradual rustiness results in imperfect contact, it is also possible that the guide tabs cannot contact the terminals in the jacks at all and causes failure of the voltage transformers because dust or flocks clog in the jacks.